The invention concerns a magnetic resonance (MR) probe head with a detecting device, comprising at least one antenna system which is cryogenically cooled by a cooling device, and a cooled preamplifier in a preamplifier housing which is disposed at a spatial separation from the detecting device, and with a thermally insulating connecting means for connecting the detecting device to the preamplifier housing, wherein the connecting means comprise at least one cooling line for supplying and/or returning a cooling fluid, and at least one radio frequency (RF) line for transmitting the electrical signals.
Cooled MR probe heads are disclosed e.g. in references [1]-[3] listed below and are used for detecting MR signals from a sample. The receiver coil is thereby cooled. This receiver coil may consist of normally conducting metal, e.g. copper or aluminium or of superconducting materials, in particular, of high-temperature superconductors (HTSC).
The MR probe head disclosed in [3] describes a system that is cooled by a cryocooler 20, wherein the cryocooler 20 is disposed at a certain separation from the actual probe head. This cryocooler 20 is usually a Gifford-McMahon cooler but may also be a pulse tube cooler. The probe head is generally cooled via a flexible transfer line 19 with continuing lines 21a, 21b, 21c, 21d which extend to a preamplifier 16 or to the receiver coil 5 via cooling lines 53a, 53b. Although the cooling lines 53a, 53b are small tubes or the like, they are represented as a line in this illustration and also in the other figures. The transfer line 19 bridges the distance to the cryocooler 20 and also keeps vibrations away from the probe head. A heat transporting medium (cooling fluid), normally cold gaseous helium, circulates in this transfer line 19. The probe head itself usually comprises at least one receiver coil 5 and at least one preamplifier 16 which are connected to each other via a rigid connecting means 15c with RF lines 52. The entire probe head is designed as one rigid unit. Such an MR probe head is shown in FIG. 9 in a room temperature bore 2 of a magnet 1 for a vertical magnet system.
This is a high performance configuration, since the RF receiver coil 5 is operated in the room temperature bore 2 of the magnet 1 at a very low temperature (e.g. 20 K), and the preamplifier 16 is operated at a such a low temperature to still ensure satisfactory function (e.g. 77 K). The RF line 52 between the receiver coil 5 and the preamplifier 16 is also at a low temperature. The temperature usually changes along the RF line 52 from 20 K to 77 K, wherein the geometry (in particular the cross-section of the cables of the RF line 52) is thereby selected such that an optimum is achieved between minimizing the RF line loss and minimizing the heat input into the cold receiver coil 5, which results from the thermal conductivity of the RF line 52. Thus, the S/N ratio of the system is optimized. After amplification with the cooled preamplifier 16, the signal is finally passed to a signal output 17 for further signal processing. The complete MR probe head may be cooled with one single cryocooler 20 (Gifford McMahon or also pulse tube cooling head).
The MR probe head may be separated from the cryocooler 20 via a coupling with coupling parts 18a, 18b for inserting and removing the MR probe head. Such a coupling is disclosed e.g. in [5] and [3]. The entire probe head including the normally large preamplifier 16 and an associated preamplifier housing 15a is however quite heavy, such that installation/removal generally requires two persons.
In particular, magnetic resonance imaging (MRI) often utilizes many different RF measuring coils. These are required to permit optimum adjustment to the test object and the particular investigation. This includes e.g. whole body coils (e.g. birdcage resonator) or surface coils. Different sizes or configurations are also used, e.g. for investigating the brain, joints, or spinal column. Array coils are moreover also increasingly used.
The above-described configuration may also be determined for different living beings, e.g. for a mouse or a rat. Clearly, this also requires scaling of the detecting device to different sizes.
This also applies for so-called micro imaging systems which are used for magnets with smaller room temperature bores but very high field strengths (up to more than 17T) in order to image smaller samples. This also requires a plurality of receiver coils.
In a fixed assembled unit of receiver coil(s) and preamplifier, each application requires one complete probe head containing the expensive cooled preamplifiers, and a large part of the cryotechnical hardware. This results in high costs for each configuration as well as great handling difficulties, since for each change the entire probe head, including the heavy preamplifier unit, must be exchanged.
It is therefore the underlying purpose of the present invention to propose an MR probe head which can be universally used and can be expanded for further measuring configurations in an inexpensive fashion.